1. Field of the Invention
The present invention relates to an image reading apparatus and, more particularly, to an image reading apparatus suitable for use in facsimile apparatus, image reader, digital copier, or the like in which a one-dimensional line sensor corresponding to a width direction of an original is provided and the image information is read while relatively moving the original whose image is to be read in the close contact relation with this line sensor.
2. Related Background Art
Hitherto, as such a kind of image reading apparatus which is called a contact type, there have been manufactured many various kinds of apparatuses in which the image on an original is projected onto a photo sensor having photoelectric converting elements onto a group of such photo sensors by using a rod lens array, a convergent fiber, or the like, thereby reading the original image.
On the other hand, in recent years, there has been developed an image reading apparatus of the type in which for the purpose of reduction in costs, further miniaturization, and the like, the rod lens array, convergent fiber, or the like is not used but a thin transparent protective layer is coated onto the photo sensor section and the original image is read while moving the original in close contact relation with the transparent protective layer on the photo sensor.
FIG. 1A shows an example of such a kind of conventional image reading apparatus. In the diagram, a photoelectric converting element section 1 is formed on an opaque layer 3 formed on a transparent substrate 2. A light L is irradiated from a light source 4 arranged on the back surface side of the substrate 2 and enters through a window portion (portion on which the opaque layer 3 is not formed) 5. The light L is reflected by the surface of an original P and received by the photoelectric converting element section 1. The following functions are required for a transparent protective layer 20: the irradiation of an enough amount of light onto the upper surface of the photoelectric converting element; the protection and stability of the semiconductor layer surface and electrode section on the upper surface of the photoelectric converting element; the prevention of deterioration in resolution which is caused by scratches and dusts due to an original or the like; and the like. However, the transparent protective layer 20 generally has a high insulative property. Therefore, when an original having image information to be read moves on the protective layer in close contact relation therewith, electrostatic charges are generated, causing inconveniences such as level shift of the signal, malfunction of a signal processing section, and the like.
Therefore, in the conventional techniques, for example, as shown in FIG. 1-B, an electrostatic shielding layer 21 made of ITO, SnO.sub.2, or the like is formed on the original contacting surface on the protective layer 20 and the potentials are held at a constant value, thereby electrically shielding the photoelectric converting element section and preventing an adverse influence by the generation of the electrostatic charges.
Or, as disclosed in U.S. Pat. No. 4,691,243 or U.S. Pat. No. 4,691,244, there has been proposed a method whereby the electrostatic shielding layer 21 is directly provided between a photoelectric converting layer 14' and the protective layer 20 and the potentials are held at a constant value, thereby preventing an adverse influence by the generation of the electrostatic charges (refer to FIG. 1-C).
However, in the conventional structure such that the electrostatic shielding layer directly comes into contact with the surface of an ordinary original as mentioned above, scratches are easily caused on the electrostatic shielding layer by the original and dusts and the electrostatic shielding layer is abraded. Thus, not only the function for a countermeasure of the electrostatic charges deteriorates but also an amount of light which is irradiated onto the photoelectric converting layer becomes unstable or the like. The function as an image reading apparatus is aversely influenced.
On the other hand, in the structure such that the electrostatic shielding layer is directly formed between the photoelectric converting layer and the protective layer, the photoelectric converting layer cannot be electrically mechanically protected, so that such a structure cannot be substantially used.
Therefore, unless all of the foregoing electrical, optical, and mechanical problems can be solved, the complete contact type image reading apparatus is not realized.